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1. Field of the Invention
The present invention relates to methods and apparatuses for backgaging during the operation of a press brake of a sheet metal bending workstation, and to sensor-based control of robotic manipulations of sheet metal workpieces and of operation of the press brake. The present invention further relates to various systems and sub-components for assisting in the operation of the backgaging and sensor-based control methods.
2. Discussion of Background and Material Information
FIGS. 1-3 illustrate, in a simplified view, an example conventional bending workstation 10 for bending sheet metal parts from a manually created program downloaded to various control devices provided within the workstation. The illustrated bending workstation is a BM100 Amada workstation.
(a) The Hardware and Its Operation
FIG. 1 shows an overall simplified view of bending workstation 10. FIG. 2 shows a partial view of a press brake 29, positioned to perform a bend on a workpiece 16. The elements shown in FIG. 2 include a robot arm 12 having a robot arm gripper 14 grasping a workpiece 16, a punch 18 being held by a punch holder 20, and a die 19 which is placed on a die rail 22. A backgage mechanism 24 is illustrated to the left of punch 18 and die 19.
As shown in FIG. 1, bending workstation 10 includes four major mechanical components: a press brake 29 for bending workpiece 16; a five degree-of-freedom robotic manipulator (robot arm) 12 for handling and positioning workpiece 16 within press brake 29; a material loader/unloader (L/UL) 30 for loading and positioning a blank workpiece at a location for robot arm 12 to grab, and for unloading finished workpieces; and a repositioning gripper 32 for holding workpiece 16 while robot arm 12 changes its grasp.
Press brake 29 includes several components as illustrated in FIGS. 1-3. Viewing FIG. 3, press brake 29 includes at least one die 19 which is placed on a die rail 22, and at least one corresponding punch tool 18 which is held by a punch tool holder 20. Press brake 29 further includes a backgage mechanism 24.
As shown in FIG. 2, robot arm 12 includes a robot arm gripper 14 which is used to grasp workpiece 16. As shown in FIG. 1, material loader/unloader 30 includes several suction cups 31 which create an upwardly directed suction force for lifting a sheet metal workpiece 16, thereby allowing L/UL 30 to pass workpiece 16 to gripper 14 of robot 12, and to subsequently retrieve workpiece 16 from gripper 14 and unload the finished workpiece.
In operation, loader/unloader 30 will lift a blank workpiece 16 from a receptacle (not shown), and will raise and move workpiece 16 to a position to be grabbed by gripper 14 of robot 12. Robot 12 then maneuvers itself to a position corresponding to a particular bending stage located within bending workstation 10. Referring to each of FIGS. 1 and 3, stage 1 comprises the stage at the leftmost portion of press brake 29, and stage 2 is located to the right of stage 1 along die rail 22.
If the first bend is to be made at stage 1, robot 12 will move workpiece 16 to stage 1, and as shown in FIG. 2, will maneuver workpiece 16 within the die space of press brake 29, i.e., at a location between punch tool 18 and die 19), until it reaches and touches a backstop portion of backgage 24. Then, a bend operation is performed on workpiece 16 at stage 1. In performing the bend operation, die rail 22 moves upward (along a D axis), as indicated by the directional arrow A in FIG. 2. As punch tool 18 and die 19 simultaneously contact workpiece 16, so that workpiece 16 assumes a relatively stable position within press brake 29, gripper 14 will release its grasp on workpiece 16, and robot 12 will move gripper 14 away from workpiece 16. Press brake 29 will then complete its bending of workpiece 16, by completing the upward movement of die 19 until the proper bend has been formed.
Once die 19 is engaged against punch tool 18, holding workpiece 16 in its bent state, before disengaging die 19 by lowering press brake 29, robot arm 12 will reposition its robot arm gripper 14 to hold workpiece 16. Once gripper 14 is holding workpiece 16, die 19 will be disengaged by releasing press brake 29. Robot 12 then maneuvers and repositions workpiece 16 in order to perform the next bend in the particular bend sequence that has been programmed for workpiece 16. The next bend within the bend sequence may be performed either at the same stage, or at a different stage, such as stage 2, depending upon the type of bends to be performed, and the tooling provided within press brake 29.
Depending upon the next bend to be performed, and the configuration of workpiece 16, the gripping position of gripper 14 may need to be repositioned. Repositioning gripper 32, shown in FIG. 1, is provided for this purpose. Before performing the next bend, for which repositioning of robot gripper 14 is needed, workpiece 16 will be moved by robot 12 to repositioning gripper 32. Repositioning gripper 32 will then grasp workpiece 16 so that robot gripper 14 can regrip workpiece 16 at a location appropriate for the next bend or sequence of bends.
(b) The Control System
The bending workstation 10 illustrated in FIG. 1 is controlled by several control devices which are housed separately, including an MM20-CAPS interface 40, a press brake controller 42, a robot controller 44, and a load/unload unit controller 46. Press brake controller 42 comprises an NC9R press brake controller, and robot controller 44 comprises a 25B robot controller, which are each supplied by Amada. Each of press brake controller 42 and robot controller 44 have their own CPU and programming environments. Load/unload unit controller 46 comprises a stand alone Programmable Logic Controller (PLC), and is wired to respective consoles provided for press brake controller 42 and robot controller 44.
Each of controllers 42, 44, and 46 has a different style bus, architecture, and manufacturer. They are coordinated primarily by parallel I/O signals. Serial interfaces are provided for transporting bending and robot programs to the controllers, each of which is programmed in a different manner. For example, logic diagrams are used to program the PLC of the load/unload controller 46, and RML is used to program robot controller 44.
(c) The Design/Manufacture Process
The overall design/manufacture process for bending sheet metal includes several steps. First, a part to be produced is typically designed using an appropriate CAD system. Then, a plan is generated which defines the tooling to be used and a sequence of bends to be performed. Once the needed tooling is determined, an operator will begin to set up the bending workstation. After the workstation is set up, the plan is executed, i.e., a workpiece is loaded and operation of the bending workstation is controlled to execute the complete sequence of bends on a blank sheet metal workpiece. The results of the initial run(s) of the bending workstation are then fed back to the design step, where appropriate modifications may be made in the design of the part in view of the actual operation of the system.
In the planning step, a plan is developed for bending workstation 10 in order to configure the system to perform a sequence of bending operations. Needed hardware must be selected, including appropriate dies, punch tools, grippers, and so on. In addition, the bending sequence must be determined, which includes the ordering and selection of bends to be performed by bending workstation 10. In selecting the hardware, and in determining the bending sequence, along with other parameters, software will be generated to operate bending workstation 10, so that bending workstation 10 can automatically perform the complete bending process.
FIG. 4 illustrates the structure of backgaging mechanism 24 of the conventional BM100 Amada bending workstation illustrated in FIG. 1. As illustrated in FIG. 4, backgage mechanism 24 comprises at least two linear potentiometers 60. for performing backgaging operations. In order to perform a backgaging operation, a robot 12 (see FIG. 1) adjusts its A dimension so that workpiece 16 is horizontal, and moves the workpiece in a positive Y direction towards backgage mechanism 24, until contact is made with at least one of linear potentiometers 60. Movement of robot 12 (and robot gripper 14) is then controlled to balance out each of the two contacted linear potentiometers 60, and to adjust the overall Y position as indicated by the output signals produced by linear potentiometers 60. In performing such an adjustment, the robot may move workpiece 16 from a first position I to a second position II, as shown in FIG. 4. When workpiece 16 is moved from location I to location II, by rotating robot gripper 14 in a -B direction, the position of workpiece 16 in the X direction will be significantly changed, by an amount .DELTA.X. For every adjustment in the position of the workpiece that is made, it is likely that the X position of workpiece 16 will be changed. This requires an additional movement by robot 12 to correct the X position of workpiece 16, and thus causes delays in the backgaging process. An additional limitation in the backgaging mechanism illustrated in FIG. 4 is that the mechanism is not designed to allow for sidegaging, i.e., gaging in the X direction of workpiece 16.